INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious This reflects a larger and perhaps insidious problem in the United States, where there’s been an erosion in trust in public health, in doctors and in the medical profession as a whole. — Joshua P. Cohen, Forbes.com, 13 June 2026 Speaking of pop music, while the new ad format is expected to have its critics, there’s a far more insidious change afoot in that Green and Pleasant Land. — Anthony Crupi, Sportico.com, 12 June 2026 But most of its failures are subtler, more insidious. — Katy Waldman, New Yorker, 10 June 2026 What makes this deal particularly insidious is the trade-off at its core. — Joe Wilkins, Futurism, 10 June 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

Currently, ocean data are gathered using massive research vessels that cannot safely navigate treacherous shallow reefs or breaking ice.

— Mrigakshi Dixit, Interesting Engineering, 9 July 2026
Projecting forward four years in this game is always treacherous, more so now than following the 2022 World Cup.

— Tom Bogert, New York Times, 9 July 2026

Definition of treacherous

Adjective

Messi’s longevity is a story of enduring brilliance but also subtle evolution.

— Charlotte Harpur, New York Times, 10 July 2026
Buyers will be able to tailor the interior with exclusive leather, Alcantara, and a choice of Comfort or Racing seats, both featuring six vertical grooves as a subtle nod to the six-speed layout.

— New Atlas, New Atlas, 10 July 2026

Definition of subtle

Adjective

Judge Ranjan identified several problems with MET’s claims, including MET’s allegation that UA engaged in false advertising by portraying Celliant as having the FDA’s blessing.

— Michael McCann, Sportico.com, 15 July 2026
Coney Barrett shared her experience bringing home a bulletproof vest and having her house swatted, or subject to false police reports.

— Emma Hinchliffe, Fortune, 15 July 2026

Definition of false

Adjective

The standout interlude is the soldiers’ visit to the island domain of Circe, a treacherous witch played with deceptive calm and a misleading air of distraction by a bone-chilling Samantha Morton.

— David Rooney, HollywoodReporter, 15 July 2026
Using a clinician’s name, image, or credentials in a synthetic endorsement without consent should be treated as deceptive practice, with liability directed toward those who commission or distribute the content.

— Henry Bair, STAT, 14 July 2026

Definition of deceptive

Adjective

Inspectors also noticed that cold foods were being held at incorrect temperatures, according to the report.

— Lillie Davidson, Fort Worth Star-Telegram, 15 July 2026
In the suit, they are referred to as a guidance counselor and principal, which the school district’s attorneys claim is incorrect.

— Austin Horn July 14, Miami Herald, 14 July 2026

Definition of incorrect

Adjective

Under rules brought in for the World Cup, the reviewable decisions and incidents now include mistaken identity when the referee shows a yellow or red card but clearly penalises the wrong player of either team.

— Stuart James, New York Times, 12 July 2026
Even when Romanzy goes off on how stupid and ugly Caleb is — and gossips that his parents abandoned him because something must be wrong with him — Mary goes along with it.

— Maggie Fremont, Vulture, 11 July 2026

Definition of wrong

Browse Nearby Words

inside tracks

insidious

insidiously

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Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 17 Jul. 2026.

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Synonyms of insidious

adjective

Example Sentences

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